Anongnad Teprek, Vincentia Poetri Artono, Weerawan Waiyawat, Aujchara Limsakul, Juwadee Shiowatana, and Atitaya Siripinyanond*

The use of spot counting on an origami paper analytical device (SC-PAD) was proposed for end point detection in titrimetric analysis. The device was designed to contain several paper layers by folding the paper into multi-layers. Each layer contained reaction zone, patterned in a circular shape. Reagents used for titration (titrant and indicator) were added onto the circular pattern of the origami PAD. For detection, sample solution was added in the top layer to allow the flow of the liquid from top to the bottom, and thereby reacted with the pre-deposited reagents on the circular reaction zone. After the reaction was completed, the folded paper was then unfolded for reading the results. Quantification was carried out by counting the numbers of circular spot that exhibited the color change. The feasibility of SC-PAD for end point detection was demonstrated for various types of titrimetric analysis. Acid-base titration was carried out for alkalinity determination. Complexometric titration using SC-PAD was applied to determine water hardness. Precipitation titration using SC-PAD was performed for chloride determination. Redox titration using SC-PAD was demonstrated for checking the level of thiosulfate concentration.

Thanks are due to the Thailand Research Fund (TRF) and Mahidol University for providing the research grant under grant number BRG 6180006. The support from Center of Excellence for Innovation in Chemistry (PERCH-CIC) is gratefully acknowledged. We also appreciate the help from Dr. Jaruwan Mettakoonpitak for sharing the source of wax printer and useful discussion. This work is related to the SDGs 4 (Quality Education) and 6 (Clean Water and Sanitation).